Voltage-dependent nonlinear resistors (hereinafter called "varistors") have been widely used as surge absorbing elements, arresters, voltage stabilizer elements, etc. Their electric characteristics are represented by the following empirical formula: EQU I/i=(V/Vi).sup..alpha. ( 1)
where I represents a current flowing through the element, V represents a voltage applied across the element, and Vi represents a voltage when the current value is i amperes. Normally, the value of Vi is selected to give a current value of 1 mA and is called the "rise-up voltage," Vima. The factor .alpha. is called a "nonlinearity coefficient," which indicates how a voltage of an electric circuit having a varistor inserted therein can be controlled. The larger the value of .alpha. is, the more excellent the voltage control characteristics are. Accordingly, except for a special use, varistors having a larger value of this coefficient are desirable. The value of Vi is determined depending upon the voltage which is to be used, and it is desirable that these values can be regulated, respectively, to given values.